Advanced Modulation Formats for Silicon-Based Optical Modulators

• US 20110044573A1
• Filed: 08/13/2010
• Published: 02/24/2011
• Est. Priority Date: 08/19/2009
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Webster, Mark, Shastri, Kalpendu, Shastri, Anujit
• Granted Patent: US 8,320,720 B2
• Time in Patent Office: Days
• US Class Current: 385/3
• CPC Class Codes: G02F 1/0121 Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0152 using free carrier effects, e.g. plasma effect
• CPC Class Codes: G02F 1/2257 the optical waveguides being made of semiconducting material
• CPC Class Codes: H04B 10/5051 using a series, i.e. cascade, combination of modulators
• CPC Class Codes: H04B 10/5053 using a parallel, i.e. shunt, combination of modulators
• CPC Class Codes: H04B 10/5055 using a pre-coder
• CPC Class Codes: H04B 10/516 Details of coding or modulation

Abstract

A silicon-based optical modulator is configured as a multi-segment device that utilizes a modified electrical data input signal format to address phase modulation nonlinearity and attenuation problems associated with free-carrier dispersion-based modulation. The modulator is formed to include M separate segments and a digital signal encoder is utilized to convert an N bit input data signal into a plurality of M drive signals for the M modulator segments, where M≧2^N/2. The lengths of the modulator segments may also be adjusted to address the nonlinearity and attenuation problems. Additional phase adjustments may be utilized at the output of the modulator (beyond the combining waveguide).

Claims

1. A silicon-based optical modulating device for converting an N-bit electrical data signal into a modulated optical output signal, the modulating device comprising

an input waveguiding section for receiving a continuous wave (CW) optical input signal;

an input optical splitter, coupled to the output of the input waveguiding section for dividing the CW optical input signal into a pair of CW optical signals;

a pair of optical waveguides coupled to the outputs of the input optical splitter, the pair of optical waveguides forming a pair of modulator arms for supporting the propagation of the pair of CW optical signals, at least one modulator arm partitioned into a plurality of M modulator segments;

a digital encoder for translating the N-bit electrical data signal into a plurality of M drive signals for the plurality of M modulator segments with M≧

2^N/2, the plurality of M drive signals selected to compensate for attenuation associated with the silicon-based optical modulating device;

an output optical combiner for combining the pair of modulated optical signals into a modulated optical output signal; and

an output waveguiding section coupled to the output of the output optical combiner for supporting the propagation of the modulated optical output signal.

2. A silicon-based optical modulating device as defined in claim 1 wherein each modulator arm is partitioned into a plurality of M modulator segments, the digital encoder providing a plurality of M pairs of drive signals.

3. A silicon-based optical modulating device as defined in claim 2 wherein the plurality of M pairs of drive signals comprise a plurality of M pairs of complementary drive signals.

4. A silicon-based optical modulating device as defined in claim 1 wherein the modulating device further comprises

a plurality of phase modulating segments disposed along the output waveguiding section and controlled by drive signal outputs from the digital encoder.

5. A silicon-based optical modulating device as defined in claim 1 wherein the plurality of M drive signals comprising a plurality of digital signals.

6. A silicon-based optical modulating device as defined in claim 5 wherein the plurality of digital signals comprise a plurality of CMOS-compatible digital signals.

7. A silicon-based optical modulating device as defined in claim 1 wherein the plurality of modulator segments are configured to exhibit a combined length L selected to provide a predetermined optical modulation amplitude (OMA) in the presence of attenuation associated with the silicon-based modulating device.

8. A silicon-based optical modulating device as defined in claim 1 wherein the plurality of modulator segments are configured to exhibit a combined length L selected to provide a predetermined extinction ratio in the presence of attenuation associated with the silicon-based modulating device.

9. A silicon-based optical modulating device as defined in claim 1 wherein the plurality of segments are configured to exhibit a combined length L, where the lengths of the individual segments are based on L/2ⁿ, n=1, 2, 3, . . . .

10. A silicon-based quadrature-amplitude modulated (QAM) optical device comprising:

an input waveguiding section for receiving a continuous wave (CW) optical input signal;

an input optical splitter, coupled to the output of the input waveguiding section for dividing the CW optical input signal into a pair of CW optical signals;

a pair of optical waveguide arms coupled to the outputs of the input optical splitter,

a first optical waveguide arm of said pair of optical waveguide arms further comprising

a first optical splitter creating a first pair of modulator arms for supporting the propagation of a first portion of the CW optical signal, each modulator arm of the first pair of modulator arms partitioned into a first plurality of M modulator segments;

a first digital encoder for translating a QAM data signal into a first plurality of M drive signals for a first plurality of M modulator segments, the first plurality of M drive signals selected to compensate for attenuation associated with the silicon-based optical modulating device; and

a first optical combiner for combining the modulated optical signals propagating along each modulator arm of the first pair of modulator arms;

a second optical waveguide arm of said pair of optical waveguide arms further comprising

a second optical splitter creating a second pair of modulator arms for supporting the propagation of a second portion of the CW optical signal, each modulator arm of the second pair of modulator arms partitioned into a second plurality of M modulator segments;

a second digital encoder for translating a QAM data signal into a second plurality of M drive signals for a second plurality of M modulator segments, the second plurality of M drive signals selected to compensate for attenuation associated with the silicon-based optical modulating device; and

a second optical combiner for combining the modulated optical signals propagating along each modulator arm of the second pair of modulator arms;

a π

/2 phase shift element disposed at the output of the second optical combiner;

an output optical combiner for combining the pair of modulated optical signals at the outputs of the first and second optical combiners into a QAM modulated optical output signal; and

an output waveguiding section coupled to the output of the output optical combiner for supporting the propagation of the QAM modulated optical output signal.